Radio-frequency generator



June 9, 1953 Filed Dec. 8, 1950 D. H. PREI$T- RADIO-FREQUENCY GENERATORP0 WER OUTPUT 7'0 LOAD 2 Sheets-Sheet l 5; INPUT 37 38 RESONATOR Paws/2INPUT FROM DE/VE 12.9.1

INVENTOR.

Donald H. Prel's ATTORNEY June 9, 1953 Filed Dec. 8, 1950 D. H. PREISTRADIO-FREQUENCY GENERATOR 2 Sheets-Sheet 2 INVENTOR. Dona/d H. Pre/s? BYM6247 ATTOQNEY Patented June 9, 1953 ITE STATES PATENT o FicE I v'RADlO-FREiiiiii GENERATOR I Donald H. Preist, Mill Valley, Califi,assignor to ,Eitel-McCullough, Inc., San Bruno, Calif., a

corporation of California Application December 8, 1950, Serial No.1'99,825

7 Claims.

My invention relates to generators of radiofrequency power usingelectron tubes, and more particularly to high-power generators using Astill further object is to provide such a generator which'may bedesignated to operate either i as an amplifier or as an oscillator.

The invention possesses other objects and features of advantage, some ofwhichwith the foregoing, will be set-forth in the. following descriptionof my invention. It is to be understood that Ido not limit myself tothis disclosure of species ofmy invention as I may adopt variantembodiments thereof within the scope of the claims.

Referring to the drawings: Figure 1 is a vertical sectional view oftheimproved R. F. generator embodying my invention;

and v I Figure 2 is a transverse sectional view taken along the planeindicated by line 2-2 of Figure 1. I, j

In terms of broad inclusion the radio frequency generator comprises aplurality of tetrodes dis-, posed in a circle about an axis and eachhavingan anode and screen grid and control grid and cathode; output andinput resonators each comprising an annular cavity extending axially ofthe circle and having inner and outer conductors, the anode of eachtetrode being electrically connected to the inner conductor of'theoutput resonator andthe cathode of each tetrode being electricallyconnected to the inner conductor of the input resonator; means includinga condenser coupling the screen grid of each tetrode to the outerconductors .ofthe resonators; and

an .annular hollow conductor extending axially of the input resonatorand encircling the inner conductor thereof. the last mentioned conductorbeing open at one end and electrically connected tothe control grid ofeach tetrode at the other end. Whenthe apparatus isoperated as anamplifier the screen grid condenser functions as an R. F. by-passcondenser and when operated as an oscillator this condenser isdesignedas a feed- 7 back device for .feeding energy from, the output resonatorto the input resonator. An important feature in my apparatus is thearrangement of the control grid line or conductor within the inputresonator, as this is'conveniently adaptable for a tetrode structurewherein the control grid terminal naturally'lies between the cathode andscreen grid terminals;

In greater detailand referring to the drawings, my radio-frequencygenerator" constructed as an amplifier comprises a plurality of tetrodesI disposed in a circle about an axis, which tubes are of likeconstructionand have like characteristics. While five tubes are shown,it is understoodthat any desired number may be employed dependingupon'the power output required. Tetrodes 1 are of conventionalconstruction having a cathode-'2, control grid 3, screen grid 4 andanode 6, 'the anode being external andall the electrodes beingpreferably cylindrical and coaxial. The preferred tube used with mycircuitry has coaxial terminals for the electrodes, such as the cathodeterminal 1 opposite the anode and thecontrol grid terminal ring 8 andscreengrid terminal ringil inter,-

posed in the envelope wall between the cathode terminal-and anode. Thissequence of'terminals on the envelope is a natural and customary terminal arrangement in tetrode type tubes. The heating structure for thecathodeis not shown but may comprise :any suitable means such asan innerfilament for heating the cathode cylinder 2 by electron bombardment, inwhich case the filament leads preferably extend out through the tubularcathode terminal 1.

The amplifier "has an output resonator Hand an input resonator l2, whichresonators comprise annular-shaped cavities that are coaxial with thetube circle and arecommon to the pluralityof tubes I. Output cavityresonator l-l is made up of an inner annular conductor comprising metalcylinders 13 joined by an end ring l4, and outer conductors comprisingmetal cylinders 1-6. These conductors thus form a pair of communicatingannular cavity sections IL-the space joining the cavity sections beinglocated adjacent the upper portions'of tubes 1. In a like manner theinput cavity resonator is made up of an inner annular conductorcomprising 'meta'l cylinders l8 joined by'an end ring IS, and outerconductors comprising metal cylinders 2! I which latter cylinders inaybe integralxwith the outer cylinders I6 of 'the output resonator.v The22, the space joining such cavity sections being located adjacent thelower portions of tubes vI.

55 Thus the annular cavities of the output and input resonators areconcentric with the axis of the tube circle, each cavity being ofU-shape in cross-section and common to the plurality of tubes I. It willalso be noted that the main sections l1 and 22 of the output and inputcavities extend axially of the tube circle so that the principalpropagation in these cavities is axial rather than radial of the tubes.

It will thus be noted that each resonator comprises two cavity sections,each section being constituted by the space between a pair of concentriccylinders. The length of each section, measured axially of the circle oftube units, is substantially greater than the width of the section,measured radially of the circle of tube units, i. e., the difference inradius of the concentric cylinders which define the section (ignoringthe thickness of the cylinders). An annulus having a greater axial thanradial dimension, measured as described is defined hereinafter as anaxially extending annulus.

Anodes 6 of the tetrodes I are electrically connected forradio-frequency current to the inner conductor of the output resonator,in the device illustrated this being a direct connection to the end ring14 which is apertured so that the anodes project upwardly into thehollow inner conductor. Suitable means for cooling the anodesmay thus beprovided in the open space of the hollow con-' ductor. In a similarmanner cathodes 2 of the tetrodes are electrically connected forradiofrequency current to the inner conductor of the input resonator,this being a direct connection to the cathode terminals 1 which projectdownwardly through the end ring IQ of the hollow conductor. Suitableleads for the cathode heater means of the several tubes may thus extendout through the hollow conductor.

Any suitable metal such as brass may be used for the various conductorsdescribed which make up the boundary walls of the cavities. For purposesof mechanical support the inner conductor of the output resonator isfactened to upper rings 23 of insulating material interposed between thecylinders l3 and 16. Likewise the inner conductor of the input resonatoris 'held in position by lower rings 24 of insulating material interposedbetween the cylinders I8 and 2|.

Screen grids 4 of the tetrodes are electrically coupled forradio-frequency current to outer conductors of the resonators. In ordertoisolate the D. C. screen grid voltage, the coupling includes an R. F.bypass condenser comprising a transverse metal plate 26. connected tothe outermost conductors I6 and 2| and a second metal plate or ring 21connected to screen grid terminal rings 9. These plates are spaced by asuitable insulating layer 28, the capacitance of this bypass condenserin the amplifier being large enough to prevent any appreciable amount offeedback of energy from the output to the input resonator. Member 26which forms the lower plate of the condenser also comprises the dividingwall between the cavity resonators, it being a metal disk extendingtransversely across the unit and fastened at the periphery to theoutermost conductors l6 and 2| which constitute the shell of thegenerator. As illustrated, this plate member is apertured to receive thetubes so that the later project partially into the upper cavity andpartially' intothe lower cavity;

From the above structure it will be seen that an output cavity circuitis provided between the anodes and screen grids of the tetrodes, andthat an input cavity circuit is provided between of the cavity sections.

the cathodes and screen grids. In order to establish the third desiredcircuit for applying the required R. F. voltage between the controlgrids and cathodes, I provide an annular open ended transmission linewithin th input resonator. This is conveniently adaptable for tetrodestructures wherein the control grid terminals 8 naturally lie betweenthe cathode and screen grid terminals. As shown, the control grids 3 areconnected to the closed end of an open ended hollow metal conductorextending axially of the input resonator and encircling the innerconductor thereof. This grid conductor comprises a pair of cylindricalwalls 29 joined by an end ring.3| connected to the control grid terminalrings 9, the end ring 3! being apertured to receive the tubes. Forpurposes of adjusting the axial length of the grid line the side wallsof the hollow conductor preferably have slideable sections 32 at theopen end. For optimum operation the length of the hollow grid conductoris preferably made equal to an integral number of half wave lengthselectrically at the operating frequency.

Adjustable means are provided for tuning the output and input resonatorsto the desired operating frequency. For this purpose a pair of annularmetal plates 33 are provided in sections ll of the output resonator, onopposite sides of the inner conductor, so as to form the upper end wallsThese plates are slideably mounted on the cylindrical walls I3 of theinner conductor, and axial adjustments is achieved by means of plungerrods 34 of insulating material projecting through supports 23. Rods 34may be connected externally to insure that plates 33 are adjusted inunison. Plates 33 are connected to the inner conductor only and havecylindrical flanges 36 closely spaced to the wall conductors It so thatthe devic also functions as a choke to confinethe R. F. and isolate theD. C. anode voltage. For this purpose the flanges 36 of the choke aremade effectively a quarter wave long at the operating frequency,telescoping sleeves (not shown) being provided on the flanges if desiredto adjust their length. Positive anode potential may thus be applied bydirect connection with the inner conductor as indicated at 31. Tuningthe output resonator is accomplished by adjusting the end plates 33 tomake the cavity sections ll the'desired length for a selected operatingfrequency, as will be readily understood.

In a like manner a pair of annular plates 38 are provided in the inputresonator, adjustable by means of plunger rods 39 for tuning to thedesired operating frequency. Here the end plates are in the nature ofshorting bars having slideable contact with both the inner conductorwalls I8 and the outer conductor walls 2|. In the apparatus illustratedthe cathodes are operated at ground potential, the positive anodepotential being applied by direct connection to the anodes as alreadymentioned. The control grid bias voltage is supplied from a suitablesource, as through a resistor 4!, and is connected to grid line 29 by awire 42 entering the resonator through a suitable R. F. choke 43. In alike manner the screen grid voltage is supplied from a suitable source,as through a resistor 44, and is connected to screen grid ring 21 by awire 45 enteringthe resonator through a suitable R. F. choke 46.

R. F. driving power may be fed into the input resonator from a suitablesource of drive by any suitable means, as by a. loop or probe. The pre-.ferred structure however, as illustrated, comprises a centrally locatedtransmission. line 41 coupled to the resonator through a slot.Transmission line 41 is made-up of an inner conductor 48 terminating atthe transverse dividing wall 26 between the resonators, and an outerconductor 49 which is a continuation of the innermost conductor 2i ofthe input resonator. Energy coupling means between the input line andresonator comprises a circular slot 50 formed by spa'cingthe inner endof conductor 2| from the. transverse wall 26. The circular arrangementof. this coupling slot is desirable because it provides uniform couplingof energy from the transmission line to the annular cavity 22.

Output power from the amplifier is preferably transferred from theoutput resonator to a suitable load by means of a transmission line 5|coaxial with the input line, and having an inner conductor 52terminating at the transverse wall 26 and an outer conductor 56 formedas a continuation of the innermost conductor I6 of the output resonator.A circular slot 51 serves to couple energy from the output resonator tothe transmission line 5|.

In adjusting the amplifier the output cavity resonator II between theanode and screen grid is tuned to resonance at the operating frequency,the plates 33 being adjusted so. that the axial length of each cavitysection I1 is an odd number of quarter wave lengths electrically. Theinput cavity resonator l2 between the cathode and screen grid isadjusted by plates 38 so that the length of each cavity section 22 isroughly an integral number of half wave lengths electrically at theoperating frequency. As already mentioned the length of the open endgrid line 29- -32 within the input resonator is also set atapproximately an integral number of half wave lengths electrically. Bythis arrangement, and by'the proper adjustment of. the lengths of thegrid line 29-32 and the input resonator 12, it is possible to achievethe desired amplitude and phases of the R. F. voltages between thecathodes, screen grids and control grids of the tetrodes.

An important feature of my annular cavity type of generator employing aplurality of tubes is thata large amount of, R. F. power can beprosustain oscillation. Thus, in the: oscillator case; the condenserassociated with the screen grid would function as. a feedback condenserrather than a bypass condenser. In other respects the structure of theR. F. generator would remain unchanged.

For purposes of illustration 1 have shown the output resonator arranged.end-to-end with the input resonator. If. it were desirable to have amore compact construction the output cavity greater than the radialdimension thereof, the

anode of. each tetrode being electrically con- F nected tol the innerconductor. of the output resonator and the cathode of each tetrode beingelectrically connected to the inner conductor of the :input:resonator,.nreans coupling the screen grid. of each. tetrode to theouter conductors of.

1 the resonators, and anannular hollow conductor extending axially ofthe input resonatorand encircling the inner conductor thereof, saidhollow conductor being open at one end and electrically connected to thecontrol grid of each tetrode at the other end.

2. A: radio-frequency generator comprising a. plurality of tetrodesdisposed in a. circle about 1 an axis and each having an anode andscreen.

duced at the higher frequencies without undue v circuit losses. In myimproved apparatus the power amplification is obtained with no greatertotal power output, as measured at the load, fora generator having nnumber of tubes is substantially n times that obtainable from a singletube in an efiicient single tube amplifier.

Another important feature of my invention is that the above mentionedadvantage of high power generation is attained with tetrode type tubes,so that the other advantages inherent in a tetrode, such as increasedpower gain, are also had.

While I have described my apparatus as an amplifier, it is understoodthat the generator may be operated as an oscillator, and that the termgenerator is employed herein, as is common usage, in the generic sense.In the latter case the input transmission line 41 would be omitted andthe capacitance of the condenser 26-2'l-28 decreased so as to providesufficient feedback of energy from the output resonator II to the inputor excitation resonator I2 to grid and control grid and. cathode, outputand input resonators each comprising an annular cavity extendingzaxiallyof. said circle and having inner and outer conductors, the axialdimension; of said resonator being substantially greater. than theradial dimension thereof, the anode of each tetrode being. electricallyconnected. to the inner conductor of the output resonator. andtheoathode of. each tetrode being. electrically connected to the innerconductor of the input resonator, means coupling the screen grid of eachtetrode tothe outer conductorsof the-resonators, and an annular hollowconductor extending axially. oiv the input. resonator and encircling theinner conductor thereof, said hollow conductor being open at one end andelectrically connected tothecontrol; grid of each-tetrode at the. otherend, the last mentioned conductor comprising telescoping: sections foradjusting the length. thereof.

3. A radio-frequency generator comprising a plurality of tetrodesdisposed in a circle about an. axis and each having an anode and screengrid and control grid and cathode, output and input resonators eachcomprising an annular cavity extending axially of said circle and havinginner and outer conductors, the axial dimension of said resonator beingsubstantially greater than the radial dimension thereof, the anode ofeach tetrode being electrically connected to the inner annularhollowconductor extending axially of p the input resonator and encircling theinner conductor thereof, said hollow conductor being open at one end andelectrically connected to the control grid of each tetrode at the otherend, and tuning means in the output and input resonators for adjustingthe axial length of said resonators.

4. A radio-frequency generator comprising a plurality of tetrodesdisposed in a circle about an axis and each having an anode and screengrid and control grid and cathode, output and input resonators eachcomprising an annular cavity extending axially of said circle and havinginner and outer conductors, the axial dimension of said resonator beingsubstantially greater than the radial dimension thereof, the anode ofeach tetrode being electrically connected to the inner conductor of theoutput resonator and the cathode of each tetrode being electricallyconnected to the inner conductor of the input resonator, means couplingthe screen grid of each tetrode to the outer conductors of theresonators, said coupling means including a condenser, and an annularhollow conductor extending axially of the input resonator and encirclingthe inner c-onductor thereof, said hollow conductor being open at oneend and electrically connected to the control grid of'each tetrode atthe other end. i

5. A radio-frequency generator comprising a plurality of tetrodesdisposed in a circle about an axis and each having ananode and screengrid and control grid and cathode, output and input resonators eachcomprising an annular cavity extending axially of said circle and havinginner and outer conductors, the axial dimension of said resonator beingsubstantially greater than the radial dimension thereof, the anode ofeach tetrode being electrically connected to the inner conductor of theoutput resonator and the cathode of each tetrode being electricallyconnected to the inner conductor of the input resonator, means couplingthe screen grid of each tetrode to the outer conductors of theresonators, said coupling means including a condenser plate connected tothe outer conductors of the resonators and a second condenser platespaced from the first plate and connected to a screen grid of eachtetrode, and an annular hollow conductor extending axially of the inputresonator and encircling the inner conductor thereof, said hollowconductor being open at one end and electrically connected to thecontrol grid of each tetrode at the other end.

,6. A radio-frequency generator comprising a plurality of tetrodesdisposed in a circle about an axis and each having an anode and screengrid and control grid and cathode, output and input resonators eachcomprising an annular cavity extending axially of said circle and hav-.

ing inner and outer conductors, the axial dimension of said resonatorbeing substantially greater than the radial dimension thereof, the anodeof each tetrode being electrically connected to the inner conductor ofthe output resonator and the cathode of each tetrode being electricallyconnected to the inner conductor of the input resonator, means couplingthe screen grid of each tetrode to the outer conductors of theresonators, an annular hollow conductor extending axially of the inputresonator and encircling the inner conductor thereof, said hollowconductor being open at one end and electrically connected to thecontrol grid of each tetrode at the other end, an output transmissionline extending axially of said circle, and energy coupling meanscomprising a circular slot communicating between said output line andoutput resonator.

'7. A radio-frequency generator comprising a plurality of tetrodesdisposed in a circle about an axis and each having an anode and screengrid and control grid and cathode, output and input resonators eachcomprising an annular cavity extending axially of said circle and havinginner and outer conductors, the axial dimension of said resonator beingsubstantially greater than the radial dimension thereof, the anode ofeach tetrode being electrically connected to the inner conductor of theoutput resonator and the cathode of each tetrode being electricallyconnected to the inner conductor of the input resonator, means couplingthe screen grid of each tetrode to the outer conductors of theresonators, an annular hollow conductor extending axially of the inputresonator and encircling .the inner conductor thereof, said hollowconductor being open at one end and electrically connected to thecontrol grid of each tetrode at the other end, an output transmissionline extending axially of said circle, energy coupling means comprisinga circular slot communicating between said output line and outputresonator, an input transmission line extending axially of said circle,and energy coupling means comprising a circular slot communicatingbetween said input line and input resonator.

DONALD H. PREIST.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,173,908 Kolster Sept. 26, 1939 2,284,405 McArthur' May 26,1942 1 2,363,641 Carlson Nov. 28, 1944 2,404,261 Whinnery July 16, 1946

